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A model for the peak frequency in the imaginary part of ${Y}_{{22}}$ (Im( ${Y}_{{22}}{))}$ based on the bias for gallium nitride (GaN) high electron mobility transistors (HEMTs) is investigated while considering both self-heating (SH) and Poole–Frenkel (PF) (electric field) effects. The peak frequency of Im( ${Y}_{{22}}{)}$ corresponds to the emission time constant of the trap in the GaN layer. In this study, ${Y}_{{22}}$ for GaN HEMTs were measured for low frequencies at which the traps respond by significantly changing not only drain voltage ( ${V}_{\text {DS}}{)}$ but also gate voltage ( ${V}_{\text {GS}}{)}$ . Because the vector network analyzer used ac with an extremely small power of −20 dBm as a signal for sensing the trap, the trap properties can be measured at a fixed dc bias. In this model, the SH effect is introduced to replace the ambient temperature in the conventional Arrhenius equation by simulating the lattice temperature. The PF effect introduces the apparent activation energy, based on the simulated electric field at the channel under the gate field edge of the drain side. The electric field is related to the voltage between the gate and drain. This model is consistent with the experimental data for a wide range of transistor biases, i.e., from the ${V}_{\text {GS}}$ near the pinch-off voltage to the ON-state condition, and the ${V}_{\text {DS}}$ in the saturation region at ambient temperatures between 23 °C and 160 °C. Furthermore, using this model, we confirmed that the PF effect dominates at a low ${V}_{\text {GS}}$ of −2 V near the pinch-off.

This article reports on the high operation voltage large-signal performance of two-dimensional hole gas diamond metal–oxide semiconductor field-effect transistors (MOSFETs) with thick atomic-layer-deposition (ALD)-Al2O3 formed on high purity polycrystalline diamond with a (110) preferential orientation. MOSFETs with a 1- $\mu \text{m}$ gate-length having a gate oxide layer of 200-nm-thick Al2O3, formed by ALD and asymmetric structures, to withstand high-voltage operations. The large-signal performances were evaluated at a quiescent drain voltage of greater than −60 V for the first time in diamond field-effect transistor (FET). As a result, an output power density of 2.5 W/mm under class-A operation at 1 GHz, which is higher than that of diamond FETs fabricated by a self-aligned gate process, was obtained. Moreover, an output power density of 1.5 W/mm was exhibited by the MOSFET when biased at a quiescent drain voltage of −40 V under class-AB operation at 3.6 GHz using an active load-pull system. This is the highest recorded value for diamond FETs at a frequency greater than 2 GHz, owing to the high-voltage operation. These results indicate that diamond p-FETs under high-voltage operations are the most suitable for high-power amplifiers with complementary circuits.

This letter reports on the development of an ${X}$ -band GaN monolithic microwave integrated circuit (MMIC) high-power amplifier (HPA) which achieves a power-added efficiency (PAE) of 54% and an output power of 70 W. Mitsubishi’s GaN field-effect transistors (FETs) with a gate length of 0.15 $\mu \text{m}$ and individual source via (ISV) structure are utilized. The developed GaN MMIC HPA demonstrates an output power of 46.1–47.4 dBm (41–56 W), a PAE of 49–55%, and a gain of 10.1–11.0 dB at the frequency range 8.5–10.5 GHz with a drain voltage of 30 V. Output power of 47.2–48.4 dBm (53–70 W), PAE of 52%–54%, and gain of 11.2–12.1 dB at the frequency of 8.5–10.5 GHz are obtained with a drain voltage of 35 V. The measured performances demonstrate the highest performance in terms of the combinations of output power and PAE compared to existing state-of-the-art ${X}$ -band MMIC HPAs.

This paper presents an AM-PM compensation of a differential power amplifier using capacitance neutralization. Gain of power amplifier is enhanced by capacitor neutralization technique[1], [2]. The AM-PM of differential power amplifier is compensated by neutralization technique since it reduces influence by the change of gm against power. The differential power amplifier with cross-coupled capacitors are fabricated with a GaN HEMT. The AM-PM of the fabricated differential power amplifier is reduced by 22 degree compared with a singlephase power amplifier without the cross-coupled capacitance. And it achieves gain of 20 dB and power added efficiency of 35 % with output power of 36 dBm at 17.7GHz.

This paper presents a wideband and high efficiency Ka-band gallium nitride (GaN) doherty power amplifier (DPA) fabricated by 0.15µm GaN-HEMT on SiC technology. The Tee-line network impedance inverter which is formed utilizing output capacitance of transistors was designed to increase operation bandwidth. Moreover, it was possible to realize the impedance inverter at millimeterwave band by using Metal-Insulator-Metal capacitor on via-holes (MIM -on-Via) structure which can decrease parasitic inductances. As a result, the fabricated 2-stage DPA has achieved a measured saturation output power of 36.1–36.5dBm, a 6dB back-off PAE of 25-27%, and a peak PAE of 26.7–31.8% in the frequency band of 26–30GHz. This fractional band is 14.6%. To the best of authors' knowledge, this performance is the widest bandwidth with high efficiency in Ka-band GaN DPA. Additionally, the measured ACPR is −31.1dBc and EVM is 3.2% at the average output power of 28dBm under 45MHz 64QAM modulated signal.

Effects of self-heating and drain voltage on buffer traps in GaN HEMTs were investigated by using low frequency S-parameter measurements. Because peaks in Y 22 imaginary parts transformed from S parameters is related with the buffer traps, the peak frequency were measured by varying ambient temperatures and drain voltages in low frequency range from 20 Hz to 100 MHz. The experimental results were reproduced well by implementing the self-heating and field enhanced electron emission effects into the Arrhenius equation.

In this paper, an X-band 100 W class high power amplifier GaN monolithic microwave integrated circuit (MMIC) is presented. A GaN high electron mobility transistor (HEMT) with a power density exceeding 10 W/mm has been developed by achieving both electric field relief and high power density to increase the amplifier output. This high power amplifier GaN MMIC is manufactured using a GaN HEMT, which has high power density. Measurement results of the two-stage amplifier MMIC show output power of 80–100 W, a power added efficiency (PAE) of 42%, and a gain of 18 dB. This result is comparable with the best state-of-the-art X-band MMIC power amplifiers ever reported. This indicates that the developed amplifier has an advantage when it is utilized in a transmit module.

This paper presents a fully-integrated two-stage GaN Doherty Power Amplifier (DPA) Module for 5G massive MIMO base stations. To overcome the size limitation of PAs in massive MIMO base-stations while meeting the wideband requirement, a new compact frequency-dependent compensating circuit with zero-phase offset in the peaking amplifier is proposed. The proposed circuit not only increases the bandwidth of the DPA, but also works as matching network, resulting in compact and flexible design. The proposed method is applied to a 10mm × 6mm two-stage GaN DPA module. Measurements show that the DPA module achieves more than 50.4% drain efficiency and 42.9% PAE over 400MHz for 3.4-3.8GHz with -50dBc ACLR under 20MHz signal with PAPR of 8.0dB, after DPD. Furthermore, for 10 carrier aggregated signal (10 × 20MHz), the DPA exhibited 43.9% PAE with -48.6dBc ACLR after DPD. The proposed DPA has efficiency comparable to DPAs with larger sizes, demonstrating size advantage of the proposed configuration.

This paper reports on a wideband Gallium Nitride (GaN) Monolithic Microwave Integrated Circuit (MMIC) high power amplifiers (HPAs) operated in S to X bands. Two band-pass non-uniform distributed power amplifiers (NDPAs) are designed to obtain wideband and high power characteristics. One is a single-ended HPA which demonstrates output power of 17 to 26 W, power added efficiency (PAE) of 24 to 44% across 2.5 to 11.0 GHz with chip size of 4.2 mm2. The other is a two-way combined HPA which demonstrates output power of 27 to 61 W, PAE of 24 to 43% across 2.5 to 10.0 GHz with chip size of 9.6 mm2.

Millimeter-wave (mm-wave) applications such as the satellite communication (Sat-com) system and the fifth-generation (5G) mobile communication system have attracted a great deal of attention. In the mm-wave applications, a GaN device which can obtain high power at mm-wave band is considered as one of the promising device for power amplifiers (PA) as shown in Fig. 1 [1] . In order to realize the attractive GaN PA, a GaN device model with high accuracy at mm-wave band is required for design of GaN PA. However, there are still some problems to obtain a large-signal model with high accuracy at mm-wave band. One of the problems is trapping effects under large-signal operation. Modeling of trapping effects on drain current and trans-conductance has been already reported in [2] .This paper presents a GaN device model including trapping effects on non-linear capacitance and a Ka-band high efficiency GaN Doherty PA designed by using the proposed model.

This paper presents the formulation and experimental validation of adaptive input-power distribution in Doherty Power Amplifiers (DPAs) using modified Wilkinson Power Divider (WPD). It will be theoretically shown that ideal power-dependent power-distribution profile for Doherty operation can be obtained by just adjusting the isolation resistor in the divider when input reflection phase of the auxiliary amplifier in power-back off range are properly set. The proposed circuit was experimentally verified by fabricating a 3.5 GHz 32 W DPA using GaN HEMT devices. Experiments showed that, by optimizing the isolation resistor, ACLR improvement of 9 dB were obtained under 8.5 dB PAPR 10 MHz LTE signal. The optimized DPA based on this technique showed an average drain efficiency of 55 % and ACLR of −50 dBc using the same signal after Digital Pre-Distortion (DPD).

We propose a new efficiency enhancement technique of Doherty power amplifiers (DPAs) using virtual short stub. In this technique, the peaking amplifier branch was utilized as an inductive short stub at output power combing point at low power level. Using this technique, it is possible to transform the low-power load impedance seen from the carrier amplifier into higher impedance than that of classical DPAs. This leads to efficiency enhancement at larger power back-off than conventional DPAs (>6dB). The relation of efficiency enhanced level and the circuit topology for DPAs with the virtual short stub are analytically derived. The proposed technique was experimentally verified by fabricating a 3.5 GHz 40 Watt Doherty power amplifier using GaN HEMTs. An average drain efficiency of 51% and adjacent power leakage ratio of −50 dBc was obtained using 10MHz LTE test signals with 8.5dB peak-to-average power ratio.

An ultra-broadband phase shifter MMIC has been developed. The phase shifter based on series all-pass networks and series inductors are loaded to the capacitors of APF. The series inductors adjusts frequency response of phase shifter. To verify the theory, the 45deg. unit bit phase shifter MMIC has been designed and fabricated. The measured phase shift is 43.4deg. +/-5.2deg. in 2GHz to 14.8GHz band.

Broadband phase shifters based on CRLH circuit have been successfully developed. Proposed phase shifters employing HPF/CRLH and CRLH/CRLH topology overcome the bandwidth limitation of the conventional HPF/LPF phase shifter. To verify this methodology, 45deg. and 22.5deg. MMIC phase shifters have been fabricated. The 45deg. MMIC phase shifter utilizing HPF/CRLH topology has achieved the phase shift of $45\text{deg}.\pm 6\text{deg}$ . in 4–16 GHz. The 22.5deg. MMIC phase shifter employing CRLH/CRLH circuit has demonstrated the phase shift of $22.5\text{deg}. \pm 3\text{deg}$ . at the same frequency band.

In this paper, GaN (gallium nitride) power amplifier for K-band satellite communication is presented. The power amplifier has 3-stage and is designed for 17.7 to 21GHz. In the design, the output matching circuit is optimized to enhance the efficiency at desired frequency, and gate bias condition is also optimized for high linearity. This amplifier shows output power of 4W and PAE (power added efficiency) of 30% with CW (continuous wave) signal. In noise to power ratio (NPR) measurement, NPR of 15dBc with PAE of 26% is achieved.

This paper has reported a Ka-band 15.5W power amplifier Monolithic Microwave Integrated Circuit (MMIC) using 0.15μm Gallium Nitride (GaN) HEMT with 15.6% fractional bandwidth. To realize a wideband power amplifier in Ka-band, a wideband band-pass filter (BPF) inter-stage matching network (ISMN) consists of the equivalent circuit parameters of inter-stage transistors is proposed. As a result, the fabricated 3-stage single-ended power amplifier MMIC using GaN-HEMT achieves a measured saturation output power (Psat) of 41.9 - 42.2dBm (15.5-16.6W) and peak power added efficiency (PAE) of 16.1 - 20.3% over 15.6% bandwidth in 26.5-31GHz under Continuous Wave (CW) operation. To the best of author’s knowledge, that 15.5W output power with 15.6% bandwidth is state-of-the art for GaN power amplifier MMIC under CW operation in Ka-band.

In this paper, a 2.5 to 10.5 GHz GaN MMIC power amplifier achieving output power of over 20 W is reported. The developed amplifier is a two-stage amplifier composed of a non-uniform distributed power amplifier for the first stage and a reactively-matched amplifier for the second stage. Measured performance of the developed amplifier shows saturated output power of 18 to 37 W (28 W on average), power-added efficiency of 19 to 40% over 2.5 to 10.5 GHz. The highest output power among MMIC amplifiers operated in a fractional bandwidth of greater than 100% is demonstrated.

Contiguous/noncontiguous carrier aggregation (CA) is one of the key features from 4G systems, which is expected to be evolved within 5G technologies. Thus, there is a need for the development of flexible, agile, and reconfigurable radio transceivers with a native support for the integration of multiple bands and multiple standards. All-digital radio-frequency (RF) transmitters have demonstrated promising potential to the design of next-generation RF transceivers. However, the simultaneous multiband transmission is still one of the key limitations of current approaches. To address this problem, this paper presents a fully digital and parallel architecture that enables the real-time design of agile and concurrent triple-band transmission. The proposed architecture is suitable for both contiguous and noncontiguous CA scenarios and considerably surpasses the state of the art in terms of frequency agility, maximum spacing between bands, and aggregated bandwidth. To enhance the system performance, an extension to a multilevel architecture based on the analog combination of pulsed waveforms is also demonstrated. Both architectures (two and seven levels) were implemented in a field-programmable gate array. Measurement results in terms of signal-to-noise ratio, error-vector magnitude, and adjacent-channel power ratio are presented and discussed. In Implementation-I, the two-level architecture presents a frequency agility from 0.1 to 2.5 GHz (with a frequency resolution of 4.88 MHz) with an aggregated bandwidth of 56.26 MHz. In Implementation-II, the seven-level design presents a frequency agility from 0.1 to 2 GHz (with a frequency resolution of 3.906 MHz) with an aggregated bandwidth of 112.5 MHz.

The ever-increasing data rate and number of connections for mobile communication offer exciting user experiences in our everyday lives. Currently, the wireless communication frontier is shifting from the current fourth generation (4G) to the forthcoming fifth generation (5G). We expect much of society to go through a revolutionary change with the advent of the 5G era-a change that will involve not only the telecommunication industry but also a wide range of vertical sectors, including automobiles, robotics, health care, factory automation, agriculture, and education.

Fifth-generation (5G) mobile communications will need to accommodate huge traffic demands in the near future. Massive multipleinput/multiple-output (MIMO) technology utilizing hundreds of antenna elements has drawn attention as a key antenna configuration for envisioned 5G applications. Realizing the massive MIMO concept of active phased-array antennas (APAAs) for 5G will require small-size, low-power-consumption, and highly accurate phase control over the wide-band frequency range, which poses significant challenges for the RF front end. This article describes prototyped highly integrated RF front ends for high super-high-frequency (SHF) wide-band massive MIMO in 5G.

A compact and broadband bridged-T phase shifter has been developed. The proposed circuit is based on a HPF/LPF phase shifter with a bridged-T circuit topology. The phase shifting circuit eliminates the SPDT switches to minimize the circuit size while keeping broadband performances. To verify this methodology, we have fabricated an 11.25deg. MMIC phase shifter whose size is 0.14mm2. The phase shifter has achieved the insertion loss of 1.2dB, and the phase shift of 11.25deg. +/-1.5deg. in 6-16GHz band. An X-band 5-bit MMIC phase shifter has also been fabricated, and achieved RMS phase error of 6deg. in 7.5-10.5GHz band with the chip size of 2.5mm2.

We report an ultra-wideband and high efficiency sub-6GHz power amplifier, which is based on periodically varied load modulation with frequency. Key novelties are frequency-periodic load modulation over multiple contiguous frequency bands combined with digitally assisted dual-input configuration, which provides optimum signal combination, magnitude and phase of dual-input signals. The amplifier using 0.15-µm GaN HEMT FETs achieved drain efficiency of 45-62% over 1.4-4.8GHz that is 110% fractional bandwidth at 6dB power back-off. This, to the best of the authors’ knowledge, is the widest fractional bandwidth reported so far for a load modulated amplifier at these frequency range. It is a very promising PA technology for 5G base station, enabling reduction of the total cost of ownership (TCO) for operators.

The fifth generation mobile communications (5G) are expected to accommodate the forthcoming huge traffic demands, and the massive multiple input multiple output (MIMO) technology utilizing hundreds of antenna elements has drawn attention as a key antenna configuration for envisioned 5G. In order to realize the active phased array antenna (APAA), three kinds of small size millimeter-wave GaN power amplifier (PA) MMICs are prototyped, and they are single-ended PA MMICs for high power and high linearity, respectively, and Doherty PA MMIC for high efficiency. To the best of author's knowledge, the prototyped PA MMICs are state-f-the art 5G amplifiers at Ka-band

Satellite communications becomes more interesting because of an increasing number of satellite launches for especially Ku-band very small aperture terminals (VSAT). The fifth generation mobile communications (5G)are also expected to accommodate the forthcoming huge traffic demands by using millimeter-wave. For such wireless communications, the needs for high power and high efficiency in GaN power amplifier (PA)have been more increasing. This paper presents the prototyped results of state-–of-the art GaN PA at Ku/Ka-bands.

In 5G mobile communication systems, superb performances, namely large system capacity, low latency and massive connection are expected. A massive multiple input multiple output (MIMO)antenna has attracted a great attraction to become a key technology to meet such 5G requirements. In this paper, we report development results of an active phased array antenna (APAA)employing a highly integrated GaAs RF frontend module at 28 GHz-band. The transmission trial of 16-beam spatial-multiplexing using the APAA with 256 antenna elements is also reported. A spectral efficiency of 63.7 bps/Hz and a downlink transmission rate of 25.5 Gbps were successfully achieved.

In this paper, 2.45 GHz ISM-Band high power and high efficiency GaN pallet amplifier for Microwave Heating is presented. To realize higher efficiency of the GaN high-power amplifier (HPA), we used both the input and output second harmonic reflection circuit in pallet amplifier. The fabricated pallet amplifier showed excellent performance, which is output power of 450 W and efficiency of 70 % with CW operation at the 2.45 GHz. To the authors' knowledge, this is one of the highest level oerformance amons ever-reoorted ones.